<template>
  <div class="spec-preview">
    <img :src="bigImg.imgUrl" />
    <div class="event" @mousemove="handleMove" ref="event"></div>
    <div class="big">
      <img
        :src="bigImg.imgUrl"
        ref="big"
        :style="{ left: bigImgLeft, top: bigImgTop }"
      />
    </div>
    <div class="mask" ref="mask" :style="{ left, top }"></div>
  </div>
</template>

<script>
import { throttle } from "lodash";
export default {
  name: "Zoom",
  props: {
    bigImg: Object,
  },
  components: {},
  data() {
    return {
      left: "0px",
      top: "0px",
      bigImgLeft: "0px",
      bigImgTop: "0px",
    };
  },
  methods: {
    handleMove: throttle(function (e) {
      // 遮罩层盒子的宽高
      const maskWidth = this.$refs.mask.clientWidth; // 200
      const maskHeight = this.$refs.mask.clientHeight; //200
      // 预览图盒子的宽高
      const preViewWidth = this.$refs.event.clientWidth; // 400
      const preViewHeight = this.$refs.event.clientHeight; //400
      // 大图的宽高
      const bigImgWidth = this.$refs.big.clientWidth; // 800
      const bigImgHeight = this.$refs.big.clientHeight; // 800

      // 计算遮罩层离预览图左边的距离
      let left = e.offsetX - maskWidth / 2;
      let top = e.offsetY - maskHeight / 2;
      // 边界处理
      if (left < 0) left = 0;
      if (left > preViewWidth / 2) left = preViewWidth / 2;
      if (top < 0) top = 0;
      if (top > preViewHeight / 2) top = preViewHeight / 2;
      // 赋值
      this.left = left + "px";
      this.top = top + "px";

      this.bigImgLeft = left * -(bigImgWidth / preViewWidth) + "px";
      this.bigImgTop = top * -(bigImgHeight / preViewHeight) + "px";
    }, 1000 / 60),
  },
};
</script>
<style lang='less' scoped>
.spec-preview {
  position: relative;
  width: 400px;
  height: 400px;
  border: 1px solid #ccc;

  img {
    width: 100%;
    height: 100%;
  }

  .event {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    z-index: 998;
  }

  .mask {
    width: 50%;
    height: 50%;
    background-color: rgba(0, 255, 0, 0.3);
    position: absolute;
    left: 0;
    top: 0;
    display: none;
  }

  .big {
    width: 100%;
    height: 100%;
    position: absolute;
    top: -1px;
    left: 100%;
    border: 1px solid #aaa;
    overflow: hidden;
    z-index: 998;
    display: none;
    background: white;

    img {
      width: 200%;
      max-width: 200%;
      height: 200%;
      position: absolute;
      left: 0;
      top: 0;
    }
  }

  .event:hover ~ .mask,
  .event:hover ~ .big {
    display: block;
  }
}
</style>
